In optical-fiber communication, time division multiplexing (TDM) and wavelength division multiplexing (WDM) are used as multiplexing techniques for increasing the number of signal channels served by a single fiber-optic line and making effective use of the line. Especially, a method known as optical time division multiplexing (OTDM) enables optical transmission at a rate higher than any electric processing speed, by dividing an optical pulse into channels, modulating data at the base repetition frequency of the pulse train before multiplexing, and performing time-division multiplexing of each channel in the optical domain.
In 40-Gb/s or higher ultrahigh-speed OTDM transmission, for instance, the pulse interval is quite smaller than in conventional transmission systems. Accordingly, light to be used as a signal must be a very short pulse having a pulse width of several picoseconds to sub-picoseconds. When OTDM transmission is implemented with those very short pulses, one of important issues is to reduce signal waveform distortions due to linear effects of the optical fiber such as chromatic dispersion and polarization dispersion.
Experimental results of ultrahigh-speed OTDM transmission reported so far include 480-km transmission at 160 Gb/s, 100-km transmission at 640 Gb/s, and 70-km transmission at 1.28 Tb/s (see non-patent documents 1 to 3). In those experiments, time-domain waveform distortions of the transmission signal were reduced by using a dispersion compensating fiber or a dispersion slope compensating fiber and controlling the dispersion value and dispersion slope of the entire transmission fiber very precisely.
The present inventors have filed patent applications on an optical transmission method and apparatus which compensate for arbitrary dispersion, polarization-mode dispersion, and waveform distortions of the signal transmitted through an optical fiber having timing jitter, simultaneously and completely by a Fourier transform (patent document 1), and on an optical pulse compressor and optical pulse generator which compress the time width of an optical pulse output from a pulse light source at a certain ratio and provide a certain pulse waveform, with very short pulse techniques used in ultrahigh-speed optical transmission and optical measurement (patent document 2).
Non-Patent Document 1
J. L. Auge, M. Cavallari, M. Jones, P. Kean, D. Watley, and A. Hadjifotiou, “Single channel 160 Gb/s OTDM propagation over 480 km of standard fiber using a 40 GHz semiconductor mode-locked laser pulse source,” Optical Fiber Communication Conference (OFC) 2002, Paper TuA3.
Non-Patent Document 2
Takashi Yamamoto, Eiji Yoshida, Koichi Tamura, Masataka Nakazawa, “640-Gb/s OTDM signal transmission over 100 km, using femtosecond pulses,” the Transactions (C), the Institute of Electronics, Information and Communication Engineers of Japan, Vol. J83-B, pp. 625-633, 2000.
Non-Patent Document 3
Takashi Yamamoto, Koichi Tamura, Masataka Nakazawa, “1.28-Tb/s OTDM transmission of femtosecond pulses over 70 km, using simultaneous compensation of third-order or fourth-order dispersion by a phase modulator,” the Transactions (B), the Institute of Electronics, Information and Communication Engineers of Japan, Vol. J84-B, pp. 1587-1597, 2001
Patent Document 1
Japanese Patent Application No. 2003-23973
Patent Document 2
Japanese Patent Application No. 2003-109708